1. Field of the invention
This invention relates generally to the field of medical devices, and more particularly to an apparatus and method for modulating flow in biological conduits automatically and remotely.
2. Description of the Background
Invasive medical procedures subject blood vessels to the risk of perforation leading to hemorrhage. Such hemorrhage often obscures the actual site of vessel damage and thereby impedes expeditious repair of the damage. In surgery, when a blood vessel bleeds profusely, the usual method of controlling the bleeding is to evacuate blood from the surgical field so that the operator may visualize the site of hemorrhage and directly repair the damage. Methods of repair range from sacrifice of the blood vessel using ligatures or cautery to repair of the vessel wall using microsurgical techniques.
If bleeding is profuse, the process of hemorrhage leads to a vicious cycle in which as hemorrhage continues, the actual site of blood extravassation is more difficult to visualize due to blood obscuring the field. Fortunately, in many open surgical procedures, suction and irrigation devices are sufficient to help the surgeon stop the bleeding.
However, in certain procedures, such as repair of intracranial aneurysms and endoscopic surgery, suction and irrigation may not be adequate to prevent hemorrhage from causing irreversible harm. Such harm may be avoided if more expeditious hemostasis is achieved.
In aneurysm surgery, preventive measures may be taken to reduce the risk of serious hemorrhage. For example, a surgeon may employ temporary surgical clips which are applied to vessels which feed the aneurysm. The clips occlude blood flow to the aneurysm while the aneurysm repair is being performed and thereby reduce the risk of severe hemorrhage during the high-risk repair procedure. The clips are removed when the repair is completed.
Endoscopic procedures rely on a transparent view of the surgical field. When bleeding occurs, it obscures the surgeon's view and may make it impossible to continue the procedure, especially if the previously transparent fluid environment within which the tip of the endoscope is navigated is clouded by blood products.
The present invention is an improved method and device for modulating flow in biological conduits. The specific application which will be described is vascular occlusion for intracranial aneurysm surgery. Briefly, the prior art entails placing a pinch-valve-type clip around a vessel to reversibly occlude flow within it. The clip is often applied using a separate instrument, called a clip applier, which reversibly and controllably grasps the clip so that the surgeon may place the clip on a vessel, actuate (i.e., "close") the clip, and then release the clip from the applier. The surgeon may use the same clip applier to engage an already-applied clip, de-actuate (i.e., "open") the clip, and then remove it from the surgical field.
Existing vascular clips are designed to be safe, effective, and to provide a relatively unobstructed view of the operative field. They are usually made of a biocompatible, non-ferromagnetic material, such as one of the stainless steels (i.e., a chromium-containing alloy), titanium, or plastic. This disclosure pertains to any clip which has the following elements:
(1) a resilient element responsible for self-closing of the clip, such as a coil spring or a leaf spring; and PA1 (2) two opposing jaw members (also known as "blades") which provide the active surfaces between which a vessel may be pinched to limit or occlude flow. PA1 (1) alpha clips resemble the Greek letter "alpha" and contain a proximal helical spiral or leaf spring on each end of which emerges an arm; the arms have extensions, known as "crossovers", which cross over one another en route to their corresponding jaws; the fulcrum of this clip lies proximally and is fixed in location; such a clip is shown in FIGS. 0A, 0B, and 0C; PA1 (2) pivot clips, in contrast to the alpha clips, have a fulcrum point in between the arms and the jaws; an example of such a configuration is seen in an ordinary clothespin; PA1 (3) mobile-fulcrum clips have a moveable fulcrum point the position of which depends on the magnitude of the gap between the jaws. PA1 (1) removal of parts of existing components of the clip, e.g., by drilling or machining; PA1 (2) creating new components of the clip which, unless otherwise specified, can be made of the same material used for the clip; PA1 (3) attaching new components to the clip or its modification, such as simple insertion in the case of inserting a hinge into its sockets, or such as welding as in the case of affixing a leaf spring to an arm. PA1 (1) J L D Atkinson, R E Anderson, and D G Piepgras (1990). A comparative study in opening and closing pressures of cerebral aneurysm clips. Neurosurgery 26: 80-85. PA1 (2) M Dujovny, N Kossovsky, R Kossowsky, A Perlin, R Segal, F G Diaz, and J I Ausman (1984). Intracranial clips: An examination of the devices used for aneurysm surgery. Neurosurgery 14: 257-267. PA1 (3) R Kossowsky, M Dujovny, and N Kossovsky (1981). Mettalurgical evaluation of the compatibility of surgical clips with their appliers. Acta Neurochirurgica 59: 95-109. PA1 (4) M Dujovny, N Kossovsky, R K Laha, L Leff, N Wackenhut, and A Perlin (1979). Temporary microvascular clips. Neurosurgery 5: 456-463. PA1 (5) L H Fink, R E Flandry, R A Pratt, and C B Early (1979). A comparative study of performance characteristics of cerebral aneurysm clips. Surgical Neurology 11: 179-186.
Some additional embodiments also rely on the presence of two opposing arm elements located proximally on the clip which permit one to open the clip by approximating these elements using, for example, a clip applier.
Further embodiments of the invention are possible by modifying a certain category of clips, known as alpha clips, which, in addition to the aforementioned elements also contain a "crossover region" where crossing elements, referred to as the "crossovers," change their relative positions depending on the degree to which the clip is open.
Besides alpha clips, the most commonly-used clips are pivot clips and mobile-fulcrum clips [illustrated on page 460 of the article by Dujovny et al., entitled "Temporary microvascular clips," and found in the journal Neurosurgery, Volume 5 (1979)]. Briefly, these three categories of clips are distinguished as follows:
While the present disclosure is described using alpha clips as an example, the first and sixth embodiments set forth below may be applied to pivot clips and mobile-fulcrum clips (the sixth embodiment requires the presence of "arms" as defined above).
The descriptions provided herein allow one reasonably skilled in the materials and mechanical arts to modify an existing vascular clip to create an embodiment of the invention. Of course, one may de novo construct a clip by combining the designs of a present clip with the modifications of the present invention specified herein. The generic elements, named "main spring," "arm," and "jaw" refer to the corresponding elements in any alpha clip, pivot clip, or mobile-fulcrum clip. In addition, the element "crossover" refers to the element between an arm and its corresponding jaw in any alpha clip.
Construction of the invention from an existing clip involves:
There is an abundance of types, sizes, and shapes of vascular clips, and it should be noted that the present invention may be applied to any of these. It should also be noted that for the present state of art, a surgeon may have a general idea of the clip to be used in a particular situation, but often will not know a priori which particular clip to use; the surgeon may rely to some degree on trial-and-error to find the perfect match for a particular patient's anatomy and physiology at a given point in time during the surgical procedure.
The following published articles are of value in understanding the present state of art:
Several earlier patents have addressed the need to controllably occlude blood vessels. For example, a device for remote occlusion of a blood vessel using a pinch valve mechanism is described in U.S. Pat. No. 2,921,584. However, the apparatus is not an automatic means for such occlusion, and the device requires a tubular connection from the occlusion valve to the actuator. The balloon-occlusion clip described in U.S. Pat. No. 3,538,917 uses balloon inflation but has similar shortcomings.
The vascular conduit tourniquet described in U.S. Pat. No. 3,786,816 is another means for temporary occlusion of blood vessels but once again does not provide for an automatic means of a non-contiguous actuator.
The micro surgical clip described in U.S. Pat. No. 4,337,774 uses a resilient rod/ratchet mechanism to control the closing force of the clip, and again fails to provide for automatic or wireless actuation of the clip.
The temporary microvascular occluder described in U.S. Pat. No. 4,478,219 discloses magnetically moving the occluding device into and out of a clamping position. However, the mechanism of actuation fails to provide automatic actuation of the device.
The inflatable vascular clamp described in U.S. Pat. No. 4,531,519 likewise lacks automatic or wireless actuation.
The atraumatic vascular balloon clamp described in U.S. Pat. No. 4,708,140 also lacks automatic or wireless actuation.
The temporary clip comprising an inflatable balloon for controlling blood flow described in U.S. Pat. No. 5,454,826 permits remote-controlled clip actuation, but once again the means of actuation is a physical link coupled to the clip mechanism which fails to automatically achieve a flow-stopping state. Also, actuation to an indefinite flow-stopping state is not automatic. What is described as automatic is the clipping pressure, but not clip activation.
Existing methods for hemostasis during aneurysm surgery are of two major types. The first is a preventive method. One example is the placement of temporary vascular clips on tributaries to potential sites of hemorrhage. With such clips in place, the chance of profuse bleeding is reduced, but the risk of stroke-like complications increases with the duration of temporary clipping. Another example of the preventive method involves having endovascular balloons in place prior to the procedure. The balloons, when activated, will occlude further blood flow to the site of hemorrhage. Once the hemorrhage is controlled, the balloons can be inactivated, thereby restoring blood flow to the brain.
Although temporary clips which can be remotely activated have been previously known, they are not commonplace in operating rooms. The main reason for this is that the means of activation is a direct physical link coupled to the clip. Such a link, such as flexible tubing, clutters the operative field and also may interfere with other operating instruments; for example, a sharp dissector may accidentally perforate the flexible tubing. Microsurgery demands maximal visualization with minimal clutter in the field; the earlier art falls short of these requirements.
The second method of hemostasis during aneurysm surgery is the direct method which involves suctioning away blood to clear the field and then identifying the source of bleeding which is then repaired by one of a number of means such as vessel sacrifice, electrocautery, vascular clipping, or vessel repair.
Existing methods for hemostasis during endoscopic surgery rely on quickly identifying the source of bleeding and using techniques such as electrocautery to repair the vessel. However, in the event of significant bleeding, the surgeon may not have the necessary time or visualization to achieve such hemostasis in which case the entire endoscopy procedure may have to be altogether aborted.
Existing methods for treating unclippable aneurysms include endovascular coiling and aneurysm wrapping. Despite these methods, aneurysm rupture can still occur. Morbidity and mortality from aneurysm rupture relate to the degree of intracranial hemorrhage. The presence of an automatic, rupture-activated clip can forestall significant bleeding and help reduce the complications of intracranial hypertension, vasospasm, and hydrocephalus from bleeding.